Babies born via Cesarean section have a different set of microbes in their digestive tracts than those born vaginally, according to a study that investigated and compared the stool samples of infants. Previous studies have linked C-sections with a higher risk of asthma, obesity, and diabetes, but the reasons weren't clear. Now researchers suggest that the heightened risk could be, at least in part, due to those microbes.

For the study, published in the Canadian Medical Association Journal, researchers had the unenviable task of sifting through the poop of 24 different 3-month-old babies. They didn't just find bacteria differences in C-section and vaginally-delivered babies, but also between those that were formula fed and breastfed.

During a vaginal delivery, babies are exposed to a whole bunch of different viruses and bacteria as they pass through the birth canal, this serves as their first immunization, jumpstarting their immune systems, enabling them to distinguish between good and bad bacteria. Babies born via C-section don't get this opportunity, and thus, their stool has fewer colonies of Escherichia and Shigella.

These are the seeding species, says [lead researcher Anita] Kozyrskyj, and lay the foundation for the next groups of microbes to come. They are critical for priming the newborn's immune system to learn which agents are potentially dangerous and which, particularly those on foods, can be given a pass.

Breast feeding also resulted in a change in microbes, with formula-fed babies showing more Peptostreptococcaceae bacteria and Clostridium difficile. In adults, C. difficile infection is associated with diarrhea and unpleasant side effects, and while babies don't seem to be as affected by the bacteria, the presence of C. difficile could push out the Escherichia and Shigella that are so critical to developing a strong and healthy immune system.

However, it's still not clear whether the differences in bacteria actually translate to the heightened risk of obesity, asthma, diabetes, and even autism. But, as the researchers of the study point out, it's worth further investigation.